Ensuring the structural integrity of pressure tubes in nuclear reactors presents a continuous problem for safety analysts.
Pressure tubes serve as the high pressure boundary of the reactor core. Over time, with normal operation, the pressure tube corrodes, resulting in the absorption of hydrogen isotopes in the material. The hydrogen isotopes then can form solid hydrides in the matrix. These hydrides are particularly brittle and can compromise the structural integrity of the pressure tube. A pressure tube with a significant concentration of hydrides present at operating conditions is at risk of hydride cracking.
Accordingly, it is important to monitor the concentration of hydrides within the pressure tube material at operating conditions.
One method of determining the concentration of hydrides is to obtain a scrape sample from the interior of the pressure tube during a shutdown. The concentration of hydrides can be determined using an appropriate Arrhenius relationship if the concentration of hydrogen is known. The sample can be analyzed by chemical methods to determine the concentration of hydrogen.
Drawbacks of the scrape method include the delay occasioned in shipping a sample to a testing laboratory and awaiting the results, the radiation risks from handling a sample from within the pressure tube, the chance of sample contamination in handling and transit, the limitation of the sampling to the surface of the tube interior, and the inability to re-sample the same area of the tube again.
Other applications also employ materials that form hydrides and that may suffer from deterioration due to the formation of hydrides. Some of these applications involve material located in hazardous environments or environments that are difficult to access. Accordingly, it would be advantageous to have a device and method for inspecting such material.